A Multimetal Broadband Metamaterial Perfect Absorber with Compact Dimension

We propose an extremely simple multiple-metal metamaterial perfect absorber (MPA). The dimension of our proposed design is only 221 nm for the visible wavelength range from 400 to 700 nm. This is comparable with past efforts on MPAs using plasmonics at the same wavelength range, whereas the plasmonic excitation is absent in our proposal. A unity broadband absorption can be achieved with ultrathin metallic films. In addition, the wavelength scalability is possible using our design, and the fully planar simple configuration facilitates large-area photonic design without the need for lithography and etching. The physics is the field penetration and the field absorption for the photons at different wavelength ranges using different metallic layers. We also show that the adjustment of the individual layer thickness is critical to attaining a perfect wave impedance matching to vacuum. The titanium (Ti), nickel (Ni), and aluminum (Al) triple-metal configuration is used to demonstrate the concept experimentally, and a close match to the theoretical result is observed. The absorption band can be further widened with more stacking layers with various metals. We believe that the proposed design is very promising in the aspects of simple processing and scalable for large-area broadband unity absorption. It thus improves the future implementation of MPAs and facilitates a wide range of relevant applications.